🎓 Law Enforcement 10 Codes: Full 10-4 Police Radio 2026

Law Enforcement 10 Codes: Complete Police Radio Code List (10-1 to 10-100)

Law enforcement 10 codes are numeric radio shorthand, such as 10-4 for "acknowledged," that police use to keep transmissions short. The codes are not standardized nationally, and FEMA's NIMS Integration Center requires plain language, not 10 codes, for multi-agency and multi-jurisdiction incidents while still allowing 10 codes in everyday department radio traffic.

Switch on any police scanner in America and within seconds you will hear it. A clipped voice says "ten-four," another voice answers "ten-twenty?" and a dispatcher cuts in with "ten-thirty-three." To outsiders it sounds like a secret language. To officers, firefighters, and EMS crews it is the fastest way to push a clear message through a crowded radio channel without burning airtime or tipping off everyone listening with a scanner app.

This page lists every law enforcement 10 code from 10-1 all the way to 10-100. We cover where the codes came from, why some departments still swear by them while the federal government wants them gone, how they vary from Florida to Texas to California, what "Code 4" actually means (hint: it is not a 10 code), and the basic radio habits every new academy cadet has to memorize before their first shift.

If you are studying for entry-level testing, sharpen up with the law enforcement how to pass law enforcement exam walkthrough or a full law enforcement practice test. Background on the profession itself sits on the main law enforcement definition primer.

What Are Law Enforcement 10 Codes?

10 codes — sometimes written as ten codes, ten-codes, or hyphenated "10-4" style — are a numeric shorthand system that police, fire, EMS, and some military radio operators use to transmit common phrases in two syllables instead of twenty. Saying "10-4" takes about half a second. Saying "I acknowledge your last transmission and will comply" takes four full seconds and chews up channel time that another officer might desperately need to call for backup. Multiply that across a hundred radio exchanges per shift and the savings become enormous.

The codes were invented in 1937 by Charles "Charlie" Hopper, communications director for the Illinois State Police. Early radio equipment had a small delay between when an operator keyed the microphone and when the carrier actually started transmitting, so the first syllable of each message was often clipped off and lost.

Hopper realized that prefixing every message with the digit "10" gave the radio time to come on-air, after which the second number — the meaningful one — would always come through clean. The system worked so well that the Association of Public-Safety Communications Officials (APCO) adopted a standardized list in 1940 and pushed it nationwide.

By the 1970s, CB radio popularity exploded the codes into pop culture. Truckers, hobbyists, and the movie Smokey and the Bandit made "10-4 good buddy" a household phrase. That same popularity is part of what eroded the codes' usefulness — once every civilian with a scanner could decode them, the privacy advantage disappeared.

Invented: 1937 by Charles Hopper, Illinois State Police.
Standardized: 1940 by APCO (Association of Public-Safety Communications Officials).
Total codes: APCO list runs 10-1 through 10-99; many departments add 10-100 and locally-defined codes.
Uniformity: not standardized — every department, county, and state has variations.
Federal policy: after Hurricane Katrina exposed interoperability failures, FEMA and DHS pushed agencies toward plain English in 2006.
Status today: roughly half of U.S. agencies still use 10 codes; the rest moved to plain language.

Why Do Police Still Use 10 Codes?

Five reasons keep the system alive in thousands of departments. Speed is the obvious one — fewer syllables, less airtime. Clarity over bad radio matters too; numbers transmit cleaner than full sentences through static, wind noise, or a partially-keyed mic. Operational discretion still has some value: while every scanner buff knows 10-4, the difference between 10-15, 10-50P, and 10-50I is not common knowledge, and on a long pursuit those small ambiguities buy seconds.

The fourth reason is tradition and academy training. Officers who spent six months at the academy memorizing the local 10 code list have it burned into muscle memory. Switching a 30-year-veteran to plain English after retirement-eligible service tends to fail. The fifth reason is tactical brevity in stress — an officer who is being beaten on the ground can squeak out "33" or "86" when she cannot string together "officer needs help immediately at the corner of..." The shortest possible code is the one she can still transmit.

Why Departments Are Dropping 10 Codes

The 2005 Hurricane Katrina response exposed a fatal weakness in the system. Mutual-aid responders from Texas, Tennessee, and Michigan flooded into Louisiana to assist New Orleans PD. Their 10 codes did not match. A Texas officer's "10-50" meant a traffic accident; a Louisiana officer's "10-50" meant officer down. Misunderstandings cost time and almost cost lives. The Department of Homeland Security and FEMA responded with a directive recommending plain language for all multi-jurisdictional operations under the National Incident Management System (NIMS).

Since 2006, large agencies like the NYPD, the California Highway Patrol, and Florida's Miami-Dade Police Department have moved their primary radio traffic to plain English, retaining only a handful of legacy codes. Smaller rural sheriff's offices that rarely interact with outside agencies have mostly kept the full code list. The result is a hybrid landscape where the answer to "do cops still use 10 codes?" is genuinely "depends which cop."

10 Codes by Usage Category

📋 Most Used Daily Codes

These are the codes a patrol officer will use or hear on virtually every shift, regardless of department.

10-4 — Acknowledged / affirmative / message received.
10-8 — In service / available for assignment.
10-7 — Out of service / unavailable (often for meal break, vehicle issues, end-of-shift).
10-20 — Location (as in "What's your 10-20?").
10-9 — Repeat / say again your last transmission.
10-6 — Busy, stand by.
10-22 — Disregard the previous message.
10-23 — Stand by / arrived on scene.
10-97 — Arrived at the scene (some agencies use 10-23 for the same).
10-98 — Assignment finished.

Master these ten and you can follow a scanner feed in most American cities.

📋 Emergency Codes

These signal high-priority calls that drop everything else on the channel. Hearing one means every available unit pivots.

10-33 — Emergency / officer in trouble / clear the channel.
10-86 — Officer needs help (this is the one no officer ever wants to call).
10-32 — Person with a gun / armed subject.
10-31 — Crime in progress.
10-34 — Riot / civil disturbance.
10-35 — Major crime alert.
10-80 — Pursuit in progress.
10-89 — Bomb threat.
10-90 — Bank alarm.
10-98 (variant) — Prison or jail break / escape.

Officers train to recognize these instantly. Failing to clear the channel for a 10-33 is treated as a serious infraction.

📋 Traffic Stop Codes

Vehicle stops generate the highest call volume in patrol work. These codes structure every stop.

10-27 — Driver's license check (run the DL through dispatch).
10-28 — License plate check (run the tag).
10-29 — Wanted / stolen check.
10-50 — Traffic accident, with suffix: 10-50F (fatal), 10-50I (injury), 10-50P (property damage only).
10-55 — Intoxicated driver / DUI.
10-57 — Hit and run.
10-58 — Direct traffic.
10-51 — Wrecker / tow truck needed.
10-52 — Ambulance needed.
10-53 — Road blocked.

A typical traffic stop radio exchange: officer calls 10-28 with the plate, dispatch returns the result, officer calls 10-27 with the DL, dispatch confirms, then officer calls 10-98 when done.

📋 Common Local Variants

Because there is no national mandate, several codes mean very different things in different jurisdictions. Always double-check the local list.

10-50 — Traffic accident in most states, but officer down in parts of Louisiana and Mississippi.
10-15 — Prisoner in custody (APCO), but civil disturbance in some Texas counties.
10-100 — Restroom break (slang/unofficial), or in some agencies an unrelated administrative code.
10-13 — Weather/road report in APCO, but in NYPD legacy: officer needs immediate assistance (NYPD has since moved to plain language).
10-14 — Suspicious person in APCO, but escort/convoy in some northeastern departments.

This is exactly why DHS pushed for plain language after Katrina — code mismatches cost lives during multi-agency response.

The Complete APCO 10 Code List

Below is the full Association of Public-Safety Communications Officials standard list of 10 codes, from 10-1 through 10-100. Treat this as a reference, not a universal truth — your local department will have its own variations. New officers should always study the agency-issued radio code card before reporting to first shift.

Codes 10-1 through 10-30 (Communication and Status)

10-1 Receiving poorly / signal weak.
10-2 Receiving well / signal good.
10-3 Stop transmitting.
10-4 Acknowledged / OK / affirmative.
10-5 Relay message to another unit.
10-6 Busy, stand by unless urgent.
10-7 Out of service / unavailable.
10-8 In service / available for assignment.
10-9 Repeat / say again your last message.
10-10 Negative / no.
10-11 Dog case (animal complaint).
10-12 Stand by / officials with you (visitors in the car).
10-13 Weather and road conditions.
10-14 Suspicious person / report of prowler.
10-15 Prisoner in custody.
10-16 Pick up prisoner.
10-17 Pick up papers / documents.
10-18 Urgent / complete assignment quickly.
10-19 Return to station / headquarters.
10-20 Location ("what's your 20?").
10-21 Telephone (call by phone, not radio).
10-22 Disregard / cancel last.
10-23 Stand by / arrived on scene.
10-24 Assignment complete.
10-25 Meet officer at location.
10-26 Detaining subject, expedite.
10-27 Driver's license information request.
10-28 Vehicle registration / plate check.
10-29 Wanted / stolen check on subject or vehicle.
10-30 Unnecessary use of radio (warning to operator).

Codes 10-31 through 10-60 (Crimes, Traffic, and Field Activity)

10-31 Crime in progress.
10-32 Person with a firearm.
10-33 EMERGENCY — clear all traffic from channel.
10-34 Riot / civil disturbance.
10-35 Major crime alert.
10-36 Correct time of day.
10-37 Investigate suspicious vehicle.
10-38 Stopping suspicious vehicle (give location and plate).
10-39 Urgent — use lights and siren.
10-40 Silent run — no lights or siren.
10-41 Beginning tour of duty.
10-42 Ending tour of duty.
10-43 Information needed.
10-44 Permission to leave the patrol area.
10-45 Animal carcass on roadway.
10-46 Motorist assist needed.
10-47 Emergency road repair.
10-48 Traffic signal repair.
10-49 Traffic signal out at intersection.
10-50 Traffic accident — suffix F for fatal, I for injury, P for property only.
10-51 Wrecker / tow truck needed.
10-52 Ambulance / EMS needed.
10-53 Road blocked.
10-54 Livestock on highway.
10-55 Intoxicated driver / DUI.
10-56 Intoxicated pedestrian.
10-57 Hit and run accident.
10-58 Direct traffic at this location.
10-59 Convoy or escort needed.
10-60 Squad in vicinity.

Codes 10-61 through 10-100 (Administrative and Special)

10-61 Personnel in area.
10-62 Reply to message.
10-63 Prepare to make written copy.
10-64 Message for local delivery.
10-65 Net message assignment.
10-66 Message cancellation.
10-67 Clear for net message.
10-68 Dispatch information.
10-69 Message received.
10-70 Fire alarm / fire reported.
10-71 Advise nature of fire.
10-72 Report progress on fire.
10-73 Smoke report.
10-74 Negative (older usage; modern equivalent is 10-10).
10-75 In contact with subject.
10-76 En route to location.
10-77 Estimated time of arrival (ETA).
10-78 Need assistance.
10-79 Notify coroner.
10-80 Chase / pursuit in progress.
10-81 Reserved (varies widely by agency).
10-82 Reserve lodging for prisoner.
10-83 Work / direct traffic at school crossing.
10-84 If meeting, ETA.
10-85 Will be delayed / running late.
10-86 OFFICER NEEDS HELP — code red, all units respond.
10-87 Pickup of evidence or subject.
10-88 Present telephone number.
10-89 Bomb threat.
10-90 Bank alarm.
10-91 Pick up subject.
10-92 Vehicle parked illegally.
10-93 Blockade established.
10-94 Drag racing in progress.
10-95 Prisoner or subject in custody.
10-96 Mental subject / psychiatric subject.
10-97 Check signal / arrived at scene.
10-98 Prison or jail break / escape.
10-99 Records indicate wanted or stolen.
10-100 Restroom / bathroom break (slang, unofficial in most departments).

Top 10 Most-Used 10 Codes (Memorize These First)

🔴 10-4

Acknowledged / affirmative / OK. The single most-used code in all of public safety. Drop into a scanner feed and you will hear it within 30 seconds.

Meaning: Message received, will comply
Replaces: Roger / copy / affirmative

🟠 10-8

In service / available. The first code an officer transmits at the start of every shift to log on with dispatch.

When used: Start of shift, after a call clears
Opposite: 10-7 (out of service)

🟡 10-20

Location. "What's your 10-20?" or "What's your 20?" is shorthand asked dozens of times per shift between units and dispatch.

Meaning: Where are you / where is it
Cultural reach: Crossed into civilian slang via CB radio

🟢 10-33

Emergency — all units clear the channel. When dispatch broadcasts 10-33, every other officer goes silent until the emergency clears.

Channel rule: Radio silence except primary unit
Triggers: Officer down, active shooter, major incident

🔵 10-50

Traffic accident, with suffix to indicate severity. 10-50F (fatal), 10-50I (injury), 10-50P (property damage only).

Suffix system: F / I / P
Triggers tow: Usually paired with 10-51

🟣 10-27

Driver's license check. Officer reads the DL number to dispatch to verify validity and pull driving history before issuing citation.

Pair: 10-28 (plate check)
Dispatch returns: Status, warrants, history

🩵 10-28

Vehicle registration / license plate check. The first code called on virtually every traffic stop before the officer approaches the vehicle.

Why first: Reveals stolen vehicle before contact
Dispatch returns: Owner, status, NCIC hits

🩷 10-86

Officer needs help. The code no officer ever wants to call. Triggers an all-hands response and is one of the few transmissions allowed to break a 10-33.

Priority: Highest possible
Response: All available units, lights and siren

🔴 10-7 / 10-8

Out of service / in service. Bookends every shift. 10-8 at start, 10-7 for meal break, 10-8 returning, 10-7 at end of tour.

Pair: Together they bracket availability
Dispatch logs: All status changes for shift records

🟠 10-22

Disregard / cancel last. Used to retract a previous request after circumstances change. Cuts wasted response time.

Example: Caller located, cancel backup
Pair: Often follows 10-66 (cancellation)

10 Codes by State: Major Variations

Although APCO published a national standard list in 1940, almost no agency adopted it exactly. Every state has its own quirks, and within states individual departments add or drop codes. Here is how some of the biggest jurisdictions handle the system.

California — 10 Codes Plus 11 Codes

The California Highway Patrol uses both 10 codes and an entirely separate set of 11 codes (for example, 11-99 means officer needs help, which is what most other states call 10-86). LAPD and most municipal California departments use a hybrid: a small list of 10 codes plus a separate numeric set called "penal code numbers" (e.g., 187 for homicide, 211 for armed robbery, 415 for disturbance, 5150 for psychiatric subject). California's reliance on penal codes alongside 10 codes makes its radio traffic some of the most code-dense in the country.

Texas — Hybrid System

Texas Department of Public Safety uses a moderate 10 code list with additional state-specific codes. The Texas 10 code list reduces some APCO codes and adds others for ranch-and-highway scenarios uncommon in urban areas (livestock on highway, abandoned vehicle on rural FM road, agricultural-equipment-related issues). Many Texas sheriffs' offices have moved closer to plain language since 2010, though smaller rural counties still use the full code list.

Florida — County-by-County

Florida has no unified statewide code list. Each county sheriff and municipal department maintains its own. The florida department of law enforcement (FDLE) state agents tend to use plain language across the state, while county deputies use traditional 10 codes. Mutual aid during hurricanes and major incidents has been a recurring problem — exactly the issue DHS flagged in 2006.

New York — Mostly Plain Language

The NYPD officially transitioned to plain English in the mid-2000s after the September 11 response demonstrated interoperability problems with FDNY and Port Authority radios. A few legacy 10 codes survive in NYPD communications (10-13 "officer needs assistance," 10-85 "need additional unit") but most traffic is conducted in plain words.

South Carolina — Active 10 Code Use

The south carolina law enforcement division (SLED) and most South Carolina county sheriff's offices retain a full 10 code list. South Carolina has not made the federal push to plain language as aggressively as Florida or California, and its rural-heavy radio traffic still leans on numeric codes.

10 Codes vs Plain Language: The Modern Debate

Pros

10 codes are faster — fewer syllables, less channel congestion, more units served per minute of airtime
Numbers transmit more clearly through static, wind noise, or weak signal than full sentences
Tactical brevity matters under stress — an injured officer can squeak out "86" when she cannot say a sentence
Some operational obscurity remains: not every scanner buff knows the difference between 10-50P and 10-50I
Tradition and academy training give experienced officers automatic recall — switching them costs months of retraining
Local codes can encode jurisdiction-specific scenarios (school crossings, livestock, specific neighborhoods) that plain language must spell out

Cons

No national standard — same code means different things in different agencies, creating mutual-aid failures
Hurricane Katrina demonstrated codes can cost lives during multi-agency response when meanings clash
Scanner apps and CB culture eroded the privacy advantage decades ago — civilians know the common codes
Plain English is universal — no training delay for outside responders, new recruits, or federal partners
DHS, FEMA, and the National Incident Management System officially recommend plain language
Younger officers raised on cellphones and texting often find plain language more natural than memorizing 100 numbers

What Does Code 4 Mean? (And Other Non-10 Codes)

One of the most common questions civilians ask about police radio is "what does Code 4 mean?" The answer is that Code 4 is not a 10 code at all. It belongs to a separate category called "Code-numbers" or "radio call codes," which sit alongside the 10 code system rather than replacing it.

The standard call codes most American agencies recognize are:

Code 1 — Routine response, no urgency, obey all traffic laws.
Code 2 — Urgent response, no lights or siren, drive slightly above normal speed.
Code 3 — Emergency response, lights and siren, proceed with caution but get there fast.
Code 4 — Situation under control, no further units needed, additional responders can disregard.
Code 5 — Stakeout in progress, stay out of the area unless requested.
Code 6 — Out of vehicle investigating, may need cover.
Code 7 — Meal break (varies by department).

Code 4 is the most popular outside the 10 codes because it shows up in countless movies and TV shows. It is shouted across crime scenes to tell responding units to slow down and stand down once the primary unit confirms the threat is neutralized.

The Phonetic Alphabet — Used Regardless of 10 Codes

One thing that survives every department's communication style is the NATO phonetic alphabet — Alpha, Bravo, Charlie, Delta, Echo, Foxtrot, Golf, Hotel, India, Juliett, Kilo, Lima, Mike, November, Oscar, Papa, Quebec, Romeo, Sierra, Tango, Uniform, Victor, Whiskey, X-ray, Yankee, Zulu. Officers use it to spell license plates, addresses, surnames, and any letter that could be confused over radio (B vs P vs D, M vs N, F vs S). Whether your department uses 10 codes, plain English, or a hybrid, you will still hear "Tag is Tango-Romeo-Foxtrot-7-2-9."

Some older departments and military-trained officers still use the LAPD phonetic alphabet (Adam, Boy, Charles, David, Edward, Frank, George, Henry, Ida, John, King, Lincoln, Mary, Nora, Ocean, Paul, Queen, Robert, Sam, Tom, Union, Victor, William, X-ray, Young, Zebra), but NATO has become the default in 21st-century policing.

10 Codes by the Numbers

📅

1937

Year invented

🇺🇸

Illinois State Police

First force to use

📡

100 (10-1 to 10-100)

Total APCO codes

🏛️

1940 by APCO

Standardized year

⚖️

2006 (DHS/FEMA)

Federal push to plain language

🚓

~50%

U.S. agencies still using 10 codes

🎬

1977 (Smokey and the Bandit)

Pop culture peak

⏱️

3.5 seconds

Average airtime saved per use

How 10 Codes Work on a Real Radio Channel

A typical radio exchange tells the story better than any explanation. Picture an officer on patrol, late afternoon, light traffic. Here is what an actual scanner feed might sound like:

"Adam-12, 10-8 from the station." (Adam-12 is in service and just left HQ.)

"10-4, Adam-12. Show 10-8." (Dispatch acknowledges and logs status.)

"Adam-12, 10-28 on plate 7-Sierra-Romeo-9-2-4." (Officer is running a plate she just observed.)

"Adam-12, 10-28 returns to white 2018 Toyota Camry, registered to Smith, John, 24 Main, valid." (Plate is clean.)

"10-4. 10-20 Eastbound Highway 101 at exit 12, 10-38 on traffic stop." (Officer giving location and announcing she is stopping the vehicle.)

"10-4, Adam-12. Stand by for backup."

(Two minutes later) "Adam-12, 10-27 on operator David, Mary, James, 1-2-3-4-5-6-7." (Running the DL.)

"Adam-12, 10-27 returns valid, no wants no warrants."

"10-4. Show me 10-98 in five." (Will clear the call shortly.)

The entire exchange takes less than two minutes and gives dispatch a complete record of the stop — start time, location, vehicle, driver, and end time — in case anything goes wrong. Now imagine that same exchange in plain language. It would take roughly twice as long and tie up the channel for other units. That is the case for keeping 10 codes alive.

Radio Communication Best Practices for New Officers

Memorize your agency's official 10 code card before first shift — there is usually a quiz at the academy

Press the microphone button and pause one full second before speaking (avoid clipping the first syllable)

Identify yourself first (unit number), then transmit the code, then any additional information

Keep transmissions under five seconds whenever possible — long messages get cut off by competing traffic

Use the phonetic alphabet for any letter that could be misheard (B/D/P/T, M/N, F/S)

When you hear 10-33, drop everything and stay off the channel until cleared

Always confirm location (10-20) at the start of any traffic stop or pedestrian contact

End every call with 10-98 (assignment complete) so dispatch can mark you available

If unsure of a code, ask dispatch in plain English — better to look new than to send the wrong message

Practice radio discipline at home with a scanner app — it builds the ear faster than classroom study

Learning 10 Codes in the Academy

Every police academy in the country teaches 10 codes during the first month of training, regardless of whether the hiring agency uses them in daily operations. The reasoning is twofold: cadets may transfer agencies later, and many neighboring jurisdictions still broadcast in codes, so an officer working a mutual-aid call needs to understand the radio traffic around her.

At the law enforcement academy, cadets typically receive a laminated pocket-card listing the agency's official codes. They are expected to memorize the entire list, with a written exam in week two or three. The exam is usually multiple choice — "What does 10-86 indicate?" — and a failing score requires remediation. By graduation, cadets are radio-fluent enough to take dispatch traffic in real time during ride-alongs.

Beyond memorizing the list, academy instructors drill on radio etiquette — pausing before transmitting, holding the mic correctly, speaking at conversational speed (not faster), and not stepping on other transmissions. These habits matter as much as code knowledge. An officer who can recite all 100 codes but mumbles into the mic is still a liability on the channel.

For applicants still preparing to enter the academy, the entry exam itself usually does not test 10 codes (it tests reading comprehension, basic math, situational judgment, and writing). Review the standard law enforcement requirements and the law enforcement how to pass law enforcement exam guide to know what is actually tested before academy starts.

10 Codes for Civilians: Should You Learn Them?

Some civilians — journalists, neighborhood-watch volunteers, scanner hobbyists, attorneys, and family members of officers — learn 10 codes to follow local radio traffic. There is nothing illegal about it. Police scanner traffic on UHF and VHF unencrypted bands is public-domain communication, and millions of people listen via apps like Broadcastify or Scanner Radio.

If you want to learn for legitimate reasons, start with the top ten codes listed above and add others as you hear them. Most online code lists are accurate for APCO standard but miss local variants — listen to your specific local agency and build a personal list. Note that more departments are moving radio traffic to encrypted digital channels (P25 Phase 2, especially for tactical and detective work), so increasingly some of the most interesting traffic is no longer publicly audible regardless of code knowledge.

The Future of Police Radio Codes

The trend is unmistakable: large agencies are moving away from 10 codes toward plain language. DHS and FEMA continue to push the change. Newer officers, raised on text messaging and natural-language voice assistants, find plain English more intuitive. Within twenty years, 10 codes will probably survive only in small rural sheriff's offices and as a tradition taught in academy.

That said, certain codes are too useful to die. "10-4" is now part of American English. "What's your 20?" appears in casual conversation. "Code 4" shows up in every cop show. Even if departments officially switch to plain language, these codes will live on as cultural shorthand long after the radio standard changes.

For officers in the field today, the practical answer is: learn both. Master your agency's current code list, but also practice transmitting in plain English. The next big incident — hurricane, mass shooting, civil unrest — may put you on the radio next to officers who do not share your code book. The ability to switch fluidly between code and plain language is now part of the job. Browse the rest of the law enforcement hub for guides on uniforms, discounts, academy training, degrees, and bilingual policing, or start the law enforcement practice test to gauge your overall readiness.

🚔 🚔 What does "10-4" mean on police radio?

Acknowledged, affirmative, or message received. It is the single most-used code in all of public safety, dating back to 1937 when Illinois State Police invented the 10-code system.

📍 📍 What does "10-20" mean?

Location — as in "What's your 10-20?" It is one of the most frequently used codes between dispatch and units, and it even crossed into civilian CB-radio slang as "What's your 20?"

🆘 🆘 What does "10-33" signal on a police channel?

Emergency — officer in trouble, clear the channel immediately. Hearing 10-33 means every available unit stops routine traffic and prioritizes the call; it is one of the highest-priority 10 codes in use.

✅ ✅ What does Code 4 mean for police (not a 10 code)?

Situation under control, no further units needed, additional responders can disregard. Code 4 belongs to a separate "call code" system used alongside, not inside, the 10-code list.

📻 📻 Who invented the 10-code system and when?

Charles Hopper of the Illinois State Police invented the system in 1937 to compress common radio phrases. APCO (Association of Public-Safety Communications Officials) standardized a national list in 1940.

🛑 🛑 What does "10-7" mean versus "10-8"?

10-7 means out of service or unavailable (meal break, vehicle issue, end of shift); 10-8 means in service and available for assignment. Officers transmit 10-8 at the start of nearly every shift to log on with dispatch.

🔟 🔟 Are the 10 codes standardized nationally?

No. Although APCO published a national standard list in 1940, almost no agency adopted it exactly. Codes vary by state, county, and even individual department — the same number can mean different things two counties apart.

🌀 🌀 Why did the federal government push departments toward plain language?

Hurricane Katrina in 2005 exposed fatal mutual-aid confusion when out-of-state responders used mismatched 10-code lists. In 2006, FEMA and DHS pushed agencies toward plain English radio traffic for multi-agency incidents.

💯 💯 What does "10-100" mean on a police radio?

Many departments use 10-100 as a locally-defined code beyond the standard APCO 10-1 through 10-99 list — commonly for a restroom break or a specific local situation. It is not part of the original 1940 APCO standard, so always confirm the local meaning.

🗣️ 🗣️ What percent of U.S. agencies still use 10 codes today?

Roughly half of U.S. law enforcement agencies still use 10 codes day-to-day, while the rest have moved to plain language following federal interoperability guidance issued after 2006.

10 Codes vs. Plain Language: What FEMA NIMS Requires

The table below summarizes the December 19, 2006 FEMA NIMS Integration Center alert (NA: 023-06), "NIMS and Use of Plain Language."

Situation	Plain language required?	What the FEMA alert says
Multi-agency, multi-jurisdiction, or multi-discipline events (major disasters, exercises)	Yes	Plain language is required for these events.
Incidents needing responders from other agencies or disciplines	Yes, tied to grants	Beginning FY 2006, federal preparedness grant funding is contingent on plain language use.
Everyday internal department communications	No	Not required, but strongly encouraged as daily practice.
Use of 10 codes in daily operations	Allowed	Does not result in the loss of federal preparedness funds.

Law Enforcement Questions and Answers

What does 10-4 mean in law enforcement?

10-4 means 'acknowledged,' 'affirmative,' or 'message received and understood.' It is the single most-used police radio code in America. An officer transmitting 10-4 is telling dispatch or another unit that the previous message was heard clearly and the officer will comply or take note. The code dates back to 1937 when Illinois State Police invented the 10 code system to compress common radio phrases into two syllables.

Are law enforcement 10 codes the same everywhere?

No. 10 codes are not standardized nationally. Each state, county, and even individual department maintains its own variations. The APCO published a recommended list in 1940 but almost no agency adopted it exactly. The same code (10-50, for example) can mean a traffic accident in Texas and officer down in parts of Louisiana. This lack of standardization is exactly why DHS pushed agencies toward plain language after Hurricane Katrina in 2006.

Why do police use 10 codes instead of just talking?

Speed and clarity. Saying '10-4' takes about half a second while saying 'I acknowledge your last transmission and will comply' takes four full seconds. Over a busy shift those savings add up to thousands of seconds of free channel time. Numbers also transmit more clearly through static and noise than full sentences, and brief codes are easier to squeak out under stress when an officer is fighting or injured.

What does Code 4 mean for police?

Code 4 means 'situation under control, no further units needed.' It is part of a separate call-code system (Code 1 through Code 7), not a 10 code. When the primary unit on scene confirms the threat is neutralized, dispatch broadcasts Code 4 to tell responding officers they can slow down or disregard. Code 3 is the opposite — emergency response with lights and siren.

What is 10-7 vs 10-8 in police radio?

10-7 means 'out of service' or 'unavailable' — used at end of shift, for meal breaks, or when an officer's car is down. 10-8 means 'in service' or 'available for assignment' — used at the start of every shift and after every call clears. These two codes bookend an officer's entire day and let dispatch track who is on the street and who is not at any given moment.

What does 10-33 mean?

10-33 means 'emergency, clear the channel.' When dispatch or an officer transmits 10-33, every other unit on the channel goes silent so the emergency traffic can flow without interruption. It is one of the highest-priority codes in the entire system, second only to 10-86 (officer needs help). Failing to clear the channel during a 10-33 is treated as a serious infraction in most departments.

What does 10-50 mean for police?

10-50 means traffic accident in most jurisdictions, usually with a suffix to indicate severity. 10-50F is a fatal accident, 10-50I is an injury accident, and 10-50P is property damage only. Be aware that in parts of Louisiana and Mississippi, 10-50 historically meant officer down — a deadly mismatch that contributed to mutual-aid problems during Hurricane Katrina and pushed federal agencies toward plain language.

Are police 10 codes being phased out?

In large agencies, yes. The NYPD, the California Highway Patrol, Miami-Dade Police, and many other major departments have transitioned primary radio traffic to plain English since 2006. The federal government (DHS, FEMA) recommends plain language under the National Incident Management System. Smaller rural sheriff's offices that rarely work mutual aid generally still use the full code list. Roughly half of all U.S. agencies still use 10 codes in some form.

Do I need to learn 10 codes for the police academy?

Yes. Almost every police academy in the U.S. teaches 10 codes during the first month of training, with a written exam in week two or three. Even if your hiring agency uses plain language, you will be tested on the academy's standard code list. Mutual-aid calls and neighboring agencies still broadcast in codes, so officers need to recognize them in real time. Most academies give cadets a laminated pocket card to memorize.

What does 10-20 mean?

10-20 means 'location.' Officers asking 'What's your 10-20?' or simply 'What's your 20?' are asking where another officer or a scene is. It is one of the most-used codes in daily radio traffic. Thanks to CB radio culture in the 1970s, 'What's your 20?' crossed into mainstream American slang and is still used in casual conversation by people who have nothing to do with law enforcement.

Does FEMA ban police 10 codes?

No. FEMA's NIMS Integration Center stated in its December 19, 2006 alert that the FY 2006 plain-language requirement does not abolish 10 codes in everyday department communications. Using 10 codes in daily operations will not cost an agency federal preparedness funds. Plain language is required only for multi-agency, multi-jurisdiction, and multi-discipline incidents such as major disasters and exercises.

When do police have to use plain language instead of 10 codes?

Police must use plain language when an incident involves responders from other agencies, jurisdictions, or disciplines, such as major disasters and joint exercises. FEMA's NIMS Integration Center says federal preparedness grant funding has been contingent on this since FY 2006. Within a single department's routine radio traffic, plain language is strongly encouraged but not required, so local 10 codes may continue.

Official Resources

APCO International — the Association of Public-Safety Communications Officials, the organization that originally standardized the 10-code list in 1940; its site has current training and communications-standards resources for dispatchers and officers.
FEMA National Incident Management System (NIMS) — the federal resource center explaining the push toward plain-language radio communication for multi-agency and mutual-aid response.
CISA SAFECOM — the federal program supporting emergency-communications interoperability across public-safety agencies, including guidance on codes versus plain language.

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